This invention relates to a wellhead assembly for use with an in-casing hydraulic drive unit for a hydraulic pumping system.
Pumping of oil from oil wells having insufficient pressure to produce by natural means is commonly practiced using what is termed a “pump jack”. This device operates at the well surface to reciprocate a sucker rod extending downwardly into the well casing and which has connected at its downhole end to a downhole well pump. Reciprocating the sucker rod actuates the downhole pump and results in an upward pumping of the oil through the well casing.
In some wells, it is advantageous to use a hydraulic pumping unit to drive the downhole pump instead of the pump jack, one major advantage being the elimination of the stuffing box which seals the reciprocating sucker rod. Hydraulically operated pumping systems are also known in the prior art. Most of these systems utilize above ground hydraulic drive equipment, see for example, U.S. Pat. No. 4,646,517, issued Mar. 3, 1987 to Wright and U.S. Pat. No. 4,305,461, issued Dec. 15, 1981 to Meyer. More recently, an “in-casing” hydraulic drive unit has been proposed, wherein the hydraulic drive unit is contained within the casing of the oil well, below the wellhead assembly. Patent literature disclosing such systems include U.S. Pat. No. 6,854,515 issued Feb. 15, 2005 to Matthew et al., CA Patent 2,415,446 to Matthews et al., issued Aug. 23, 2005, U.S. Patent Application No. 2006/0222525 A1, by Lacusta et al., published Oct. 5, 2006, CA Patent 2,490,846 issued Dec. 19, 2006 to Sabre Machining Ltd., and U.S. Pat. No. 4,745,969 issued May 24, 1988 to Henderson. However, these “in-casing” systems do not disclose wellhead assemblies for adequate wellhead control and/or control over the hydraulic supply lines with isolation from the production.
A wellhead assembly is needed for use with in-casing hydraulic pumping systems in order to provide for adequate well control. For example, in U.S. Pat. No. 6,854,515, the wellhead control is described only in passing, noting that a landing spool is bolted onto the wellhead and the hanger of the wellhead hydraulic drive unit will then be landed within the landing spool. Alternatively, in U.S. Pat. No. 6,854,515, it is noted that the wellhead hydraulic drive unit can be directly bolted to the wellhead by means of a flange where well control precautions are not an issue. Neither wellhead control approach is shown in the patent. Thus, there is a need for a wellhead assembly to provide adequate well control for use with a hydraulic pumping unit. Such well control is often needed in environments with tight regulatory controls on emissions.